illegal user msgs????

[Repo]

can someone plz explain to me what they are and how i can stop them, for some reasons when i join a server i get disconnected then in console it says "illegal user msg (then random number here)"
it doesnt happen all the time, but it does when happen when im needed lol,, if you could ty.!

[FluxCapacitor]

Same thing happened to me on a server, they said that HLguard said i was cheating and was kicking me :/